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My application is having memory problems, including copying lots of strings about, using the same strings as keys in lots of hashtables, etc. I'm looking for a base class for my strings that makes this very efficient.
I'm hoping for:
My platform is g++ on Linux (but that is unlikely to matter).
Do you know of such a library?
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In computer science, string interning is a method of storing only one copy of each distinct string value, which must be immutable. Interning strings makes some string processing tasks more time- or space-efficient at the cost of requiring more time when the string is created or interned.
In C++, an extra byte is appended to the end of string literals when they are stored in memory. In this last byte, the number 0 is stored. It is called the null terminator or null characters, and it marks the end of the string.
If your program needs to create a string of varying lengths then you'll have to allocate the memory yourself using malloc. In duplicating a string, s, for example we would need to find the length of that string: int len = strlen(s);
copy-on-write (I think this comes for free in nearly all std::string implementations)
I don't believe this is the case any longer. Copy-on-write causes problems when you modify the strings through iterators: in particular, this either causes unwanted results (i.e. no copy, and both strings get modified) or an unnecessary overhead (since the iterators cannot be implemented purely in terms of pointers: they need to perform additional checks when being dereferenced).
Additionally, all modern C++ compilers perform NRVO and eliminate the need for copying return value strings in most cases. Since this has been one of the most common cases for copy-on-write semantics, it has been removed due to the aforementioned downsides.
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If most of your strings are immutable, the Boost Flyweight library might suit your needs.
It will do the string interning, but I don't believe it does copy-on-write.
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Andrei Alexandrescu's 'Policy Based basic_string implementation' may help.
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Take a look at The Better String Library from legendary Paul Hsieh
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